This invention relates to a reader for coded surface acoustic wave devices which reader is particularly useful for controlling access to a protected area.
Access control systems have been utilized in the past to restrict access to a protected area to only those who are authorized to enter. Such systems usually involve a card reader into which a coded card is inserted and read. The code on the card, which may periodically be changed, may be identical for all those wishing to enter the protected area or each person who is authorized to enter the area may be assigned his own personal code which again may be periodically changed. Upon the recognition of a permissible code, the card reader and associated system will permit access to the protected area.
These card readers usually comprise a cabinet for housing the access control system or subsystem thereof and typically have a plurality of sensing fingers for making contact with the cards inserted into the reader and for sensing the code on the card to allow access to the protected area if the card carrier has the proper code. To gain access to the protected area, the card is inserted into a slot in the cabinet which results in the wiping over of the surface of the card by the sensing fingers during both this insertion and the subsequent withdrawal of the card.
Because these typical prior art card readers involve contact between the reader and the card, there is substantial wear and tear on both the reader and the card which adversely affects the reliability of the overall system. Moreover, since there is direct contact between the reader and the card, and since card readers used in access control systems are quite often located outdoors, certain elements of the card reader, notably the sensing fingers, are exposed to the vageries of weather and are, therefore, subject to corrosion which again adversely affects the reliability of the system.
The present invention relies upon the use of a surface acoustic wave device in a code reading system to solve many of the problems of the prior art card readers. Because a coded surface acoustic wave device is used in conjunction with a reader, there is no necessity of contact between the reader and the device which eliminates the wear and tear of the prior art card readers and there is no necessity for any exposed elements which eliminates the weather-proofing problem of the prior art card readers. Moreover, a surface acoustic wave device reading system is less costly than many prior art card readers while still providing for a large number of codes which can be recognized by the system.
Although it is important to the reader of the present invention and to the access control system in which the present invention can be utilized that the surface acoustic wave device be coded, the specific method chosen to code the surface acoustic wave devices is not essential to the practice of the present invention. Indeed, several methods are known by which surface acoustic wave devices can be coded for such uses as fixed code filters, programmable matched filters, delay lines, multiplexers, storage, and commercial identification. Neither these devices, nor the types of the codes they employ, nor the manner in which they are encoded are important to the reader of the present invention nor to access control systems of the present invention.